The steering system for many articulated vehicles have neutralizer or limit valves to shift a steering valve to a neutral or blocking position to hydraulically stop the steering movement prior to the mechanical stops attached to the frames of the vehicle making contact. Such a steering system usually includes a pilot operated steering valve to control the flow of pressurized fluid from a steering pump to the steering actuator with the steering valve being moved to a steering position by pilot fluid directed thereto through a pair of pilot lines which in many cases are connected to a hand metering unit (HMU). The neutralizer or limit valves of such systems are disposed in the pilot lines and are actuated to block the pilot flow from the steering valve when the frames reach a predetermined steering angle. The steering valve thus returns to a neutral or fluid blocking position to hydraulically lock the actuators to maintain the frames at the desired steering angle.
Some of the smaller articulated vehicles have a hydrostatic steering system in which the HMU directly controls the flow of pressurized steering fluid from the steering pump to the steering actuators without the use of a separate steering valve. The hydrostatic steering system of some of such vehicles are of the load sensing type in which the fluid supply is provided by a load sensing variable displacement pump which provides fluid to the HMU in the quantity and at the pressure demanded by the HMU. One of the problems encountered therewith is that since the hydrostatic steering systems do not have any pilot lines, the neutralizer arrangement noted above will not work therein. However, it is still desirable to hydraulically stop the steering movement of the frames before the engagement of the mechanical stops.
The present invention is directed to overcoming one or more of the problems as set forth above.